The subject matter disclosed herein relates to optical luminaires for generating light and in particular to a luminaire that eliminates die imaging caustics such as undesirable non-uniform concentrations of light, and improves spatial uniformity by using means for twisting a profile of a bundle of light rays.
Lighting devices, such as incandescent or halogen sources for example, are used in many retail and product display venues due to the high light directionality and high color rendering index (“CRI”) they can achieve. These lighting devices use a standard receptacle, such as MR-16 for example, to receive a light source. The designation MR-16 stands for “Multifaceted Reflector” where the “16” represents the number of eighths of an inch for the outer diameter of the lighting device, in the case of MR-16 the diameter is 2 inches.
A CRI for a lighting device is an average of the color shift exhibited by the light reflecting from a color reference grid, typically comprised of 8 or 14 tiles. This reflected light is compared to the same grid reflecting an ideal illuminant. The ideal illuminant is a plankian radiator for color temperatures less than 5,000° K and a daylight source spectrum for sources having color temperatures of 5,000° K and greater. It is desirable to have a CRI of at least 90 for lighting applications such as a retail display for clothing and food or for applications requiring attentive examination of detailed features, such as illumination in a surgical operating room.
The MR-16 lamp is a light source typically used for highlighting, product display and where attentive examination of detailed features is desired. Exemplary power levels of an MR-16 lamp are 20, 35, 50 or 72 watts. A typical 20 W halogen MR-16 lamp producing 300 lumens has a disadvantage of a short life span and poor luminous efficacy. The typical lifetime of a halogen MR-16 lamp is 2,000 hours, while the typical luminous efficacy is 15-23 lumens/watt.
While existing luminaires are suitable for their intended purposes, improvements may be made in providing a replaceable luminaire having similar CRI output light characteristics and light distribution patterns to existing lighting devices while increasing luminous efficiency and life-span.